S&W revolver armorers are told to check the "timing" (carry up) in the New Model DAO 5-shot revolvers using DUMMY rounds in the charge holes.

This is because the cylinders lack the older (and breakable) cylinder pins to hold the extractor. The ammunition cases (DUMMY rounds for bench checks) provide the pressure to hold the extractor properly positioned in the cylinder. (After all, the extractor is cut with dummy rounds in the charge holes so the ratchets are positioned to provide proper carry up with cases in the charge holes.)

With the cylinder charge holes filled with DUMMY rounds, and NO pressure is being applied to the cylinder (in other words, don't touch or create any drag on the cylinder), the trigger is slowly pulled to the rear. Slowly ... not slooooooowwwwly.

If you're holding the gun with your right hand, and pulling the trigger with your right index finger, then your left hand can hold the barrel to stabilize the gun during the slow trigger pull ... not the cylinder.

The cylinder stop's ball should engage each cylinder stop notch before the hammer falls.

Repairing a "does not carry up" condition (or, a "timing problem", if you'd rather) has a couple of possible corrections.

The hand can be replaced with the next larger (oversize) hand available for that model. Oversize hands can vary, and sometimes using a micrometer to identify the next closest size to the original one is handy.

The use of an oversize hand, however, might also create a condition known as a "long ratchet". That condition can be repaired (file, knowledge & some experience).

If the larger hand doesn't correct the DA carry up, then the extractor will have to be replaced. S&W makes a cutting hand/arm for that purpose, which is sold to revolver armorers (a lever bar welded to a trigger, into which is installed a cutting hand - to cut the steel ratchets - and which replaces the actual trigger for the purpose of cutting each ratchet in the specific revolver model). Obviously, this is a repair best left to the factory repair techs, or a gunsmith (or trained armorer) who has the proper tools.

Cutting a new extractor is always done using the original stock hand, BTW.

Also, the use of an oversize hand which is too wide can create binding, and get you into territory where the frame's hand window might require adjustment ... which means you may risk damaging the EXPENSIVE frame (serial numbered part of the gun).

Sometimes proper cleaning of a revolver can "restore" proper function, though, so it might be a good idea to have the gun examined by a gunsmith, to make sure a "repair" isn't needed (but just a good cleaning & lubrication).

Now, pulling back on the trigger and checking to see if the cylinder can turn and produce "clicking" is another test (known as checking "hand sing"), and it can be done with pressure to different parts/sides of the trigger ... but it's also not something that is probably easily understood, done (or addressed) by the average revolver owner.

Got a good gunsmith nearby who can help you inspect/check whatever revolver it is you're wondering about?